Viruses in the family Bunyaviridae are significant pathogens of humans and animals. Temperate zone mosquito-borne bunyaviruses, for example - LaCrosse encephalitis virus, are transovarially transmitted (TOT) and overwinter in diapaused eggs of the vector. TOT of bunyaviruses is very efficient in comparison to viruses from other major arbovirus families, such as alphaviruses and flaviviruses, even though the alternate viruses are virtually pantropic (with the exception of ovarian follicles) in infected adult vectors. The goal of this research is to delineate the molecular bases of efficient TOT of bunyaviruses by mosquito vectors. Vector and viral molecular determinants of LAC virus productive TOT by Aedes triseriatus will be determined using viral and vector gene and gene product specific probes and monoclonal antibodies, respectively. Bunyaviruses utilize certain unique replicative strategies, which are not found in alphaviruses and flaviviruses. Bunyaviruses are "cap scavengers"; they require host mRNA to prime their own transcription. Bunyaviruses may require ongoing host translation for efficient synthesis of viral full length mRNAs. Bunyavirus replication in vector cells is apparently modulated by N protein encapsidation of host viral RNA. These unique viral replication mechanisms could be determinants of efficient TOT of bunyaviruses. Studies will be conducted to determine if co-regulation of vector and viral transcription and translation modulate bunyavirus replication and perhaps virulence during critical mosquito developmental stages, such as follicular resting stages and diapause. Alternate molecular mechanisms, which could account for efficient TOT of bunyaviruses, will also be investigated. These studies will provide considerable information concerning the mechanisms involved in arbovirus maintenance and amplification in nature. Such information could theoretically be exploited for prevention and control of arbovirus infections in humans, which would be of significant public health importance.